Electrowinning process for the improved recovery of metal

ABSTRACT

Metal, particularly copper, is extracted simultaneously from both its oxide ores and its sulfide ores and its sulfide ores by an electrowinning operation which is normally used only in conjunction with the extraction of metals from oxide ores. It is found that an addition of copper sulfide particles to the electrochemical bath, which has been prepared by solubilization of the metal from the metal oxide with sulfuric acid, significantly increases the efficiency of the metal extraction process.

United States Patent Tributsch et al.

1451 Oct. 28, 1975 ELECTROWINNING PROCESS FOR THE IMPROVED RECOVERY OF METAL Inventors: Helmut Tributsch; Federico Fanta, .both of Santiago, Chile Corporacion de Fomento de la Produccion, represented by Comite de Investigaciones Technologicas, Santiago, Chile Filed: Aug. 30, 1973 Appl. No.: 392,935

Assignee:

Foreign Application Priority Data Oct. l3, 1972 Chile 709-72 US. Cl.. 204/105 R; 204/1 l2;l08;l09;l19;l20 Int. CL C25C 1/12; C25C 1/20; C25C 1/l4; C25C l/ll Field of Search 204/lO8, 105 R, H9, 112, 204/109, 120

References Cited UNITED STATES PATENTS 5/1957 Tuwiner 204/108 3,464,904 9/1969 Brace 204/105 R 3,673,061 6/1972 Kruesi 3,736,238 5/1973 Kruesi et al.. 3,755,104 8/1973 Kruesi 204/105 R Primary ExaminerR. L. Andrews Attorney, Agent, or FirmKarl W. Flocks [5 7] ABSTRACT 20 Claims, No Drawings ELECTROW INNING PROCESS FOR THE -IMPROVED RECOVERY OF METAL FIELD OF THE INVENTION The present invention relates, in general, to the recovery of metals (Copper, Cobalt, Nickel, Silver) by electrochemical deposition of such metal from its solution by application of a given voltage to the electrodes of an electrolytic cell, i.e. electrowinning. In a particular case, the present invention relates to the recovery of copper by electrochemical deposition from its solution in the presence of copper sulfide.

BACKGROUND OF THE INVENTION The processing of oxide minerals for the recovery of metal is carried out, in the conventional way, by the following steps described for the most general method:

a. Mining and crushing b. Leaching including the solubilization of metal by an acid agent, such as sulfuric acid. This leaching action involves, in the case of copper oxide minerals, solubilization of a number of cations including copper, iron, aluminum, manganese, etc. Sometimes the contaminant cations do not disturb the recovery of the desired metal from the solution, but in some other cases they do and certain techniques are commonly applied to minimize the effects of the contaminant cations.

. Recovery of the metals, e.g. coppers, from solution is usually carried out in alternative stages, such as by iron precipitation, gas precipitation, solvent extraction, etc., and also by:

Electrowinning: In this process an electric current is applied to electrodes submerged in the acid leaching solution. The electric current, under appropriate conditions, promotes the selective deposition of a selected, usually the desired, metal at the cathode. This process is carried out in electrolytic cells containing a number of anodes and cathodes submerged in the solution. In general the anode is insoluble in the leaching solution and the cathode is a starting sheet of relatively pure metal, such as of the metal to be recovered.

Electrowinning is a very common process used for the recovery of copper, and it is adversely affected by problems caused by the presence of ions (Fe, Al, Mn, etc.), solids in suspension, and other impurities. One of the relevant problems is caused by oxidizing ferric ions. In general, their presenceprovides action which can be shown in the following reaction:

Cu F2 60 CuSO 2 FeSO, (cathodic) In other words, the ferric ion action dissolves deposited copper and ferric ion is reduced to ferrous. This means that additional electric current must be used to again deposit dissolved copper which consequently causes a low current efficiency in the cell. This so called ferric corrosion added to the negative action of other ions, to solids in suspension, and other impurities often results in a low efficiency and a metal deposit of poor quality with respect to metal purity, density, adherence, etc.

In general a substantially different procedure is normally used to recover metal from its sulfide minerals. Thus, in general, copper sulfide minerals are commonly processed by the following steps:

a. Mining b. Crushing, grinding and milling c. Concentration. The purpose of this stage is to yield a final paste or powder containing a high percentage of a sulfide metal recovered. Many alternative concentration procedures are possible: flotation, gravity, magnetic electrostatic concentration and others are used, but the most widely used is flotation. Flotation copper concentrates commonly contain copper in the range of 25-55%. The mineral species constituents are mainly: copper sulfides, copper and iron sulfides, silica and other gangues.

d. Smelting (commonly in a reverberatory furnace).

e. Conversion.

f. Fire refining, or

g. Electrolytic refining-cathode smelting in their commercial shapes.

There is no knowledge of an electrometallurgical method for the simultaneous recovery of metal in the same electrolytic reactor from solutions containing the metal as ions and solid sulfide compounds of the same cation.

SUMMARY OF THE INVENTION It is, accordingly, an object of the present invention to overcome deficiencies in the prior art, including those present in the operations above described.

It is another object of the present invention to provide for the improved provision of metal in pure form.

It is another object of the present invention to provide for the improved extraction of metals from their ores.

It is another object of the present invention to provide an improved process for extracting copper from its ores.

It is another object of the present invention to provide an electrometallurgical method for the simultaneous recovery of a metal, such as copper, in the same electrolytic reactor, from solutions containing the metal as ions with solid sulfide compounds of the same cation dispersed or suspended in the electrolytic solutions.

These and other objects and the nature and advantages of the instant invention will be more apparent from the following detailed description of an embodiment relating to the extraction of copper, it being understood that reference to copper is made as an example and without being a restriction on the generality of the invention.

DETAILED DESCRIPTION OF EMBODIMENTS Copper is deposited in the electrochemical precipitation according to the reaction: 1

cuso, H 0 H 80, Cu a 0 At the same time copper is redissolved according to the reaction:

Cu Fe (SO CuSO, 2 Feso, This latter reaction reduces the efficiency of the process. It would be convenient to introduce a chemical reaction to keep iron, and other oxidizing agents, reduced to avoid electron exchange reactions at the cathode. To accomplish this result copper sulfide particles are added to the electrowinning electrolyte prepared from the solubilization of oxide minerals. The following reaction will proceed:

2i=e,(so. Cu S p 20150, 4Feso, S"

In this reaction iron is reduced and copper sulfide is decomposed.

The above reaction is relatively slow. If, however, copper sulfide, in the electrochemical cell, is kept in suspension, so that particles will hit the electrodes, the

dissolution reaction of copper sulfide is considerably accelerated. The reason for this is that copper sulfide particles, which are semiconductors, absorb electrical charges at the electrodes and initiate favorable electrochemical reactions. One of the main reactions is the following: at the surface of copper sulfide particles, which pick up positive charge (a process which is equivalent to the generation of chemical missing bonds in the copper sulfide surface), an anodicelectrochemical reaction proceeds which liberates copper ions and dissolves the copper sulfide crystals. Oxidizing agents like iron support this reaction and are thereby reduced.

To some extent, accelerated dissolution in the presence of iron can be understood as a chemical reaction as described above, but facilitated by the lack of some chemical bonds in the copper sulfide crystal as the result of the presence of positive electrical charges. The electrochemical dissolution of copper sulfide can also proceed in the absence of oxidizing agents too.

The following situation, resultingfrom the maintenance of copper sulfide in suspension in an electrowinning solution, can therefore be observed:

a. The ordinary electrowinning process proceeds undisturbed.

b. Copper sulfide particles are dissolved and ex:

tracted copper is directly deposited.

c. The efficiency increases because of the involvement of oxidizing agents in the copper sulfide dissolution reaction.

Energetic dissolution of copper sulfide is obtained to a good extent due to a diminished oxygen evolution, an increase of reduction of iron or other oxidating agents and oxidation of copper sulfide at the anode. The anodic current has to be sufficiently high to warrant a good efficiency of this process; however, it is found that the ordinary electrodeposition of copper from electrolyte solution maintains this current. The presence of copper sulfide particles in the solution has the favorable result of increasing the efficiency of agitation.

The process of the present invention has been carried out successfully, as will be seen from the following examples which are offered illustratively. The copper obtained is physically and chemically equivalent, from a Anode (insoluble): 5 mm thick, Pb-Sb-Ag alloy (95% 14% 1%) (Any suitable passive anode may be used). Cathode (starting sheet): 0.l mm thick electrolytic copper foil, analytical grade.

5 Energy: Hewlett Packard 6206 B power source. Current was recorded in a Methrem recorder and voltage measurement was carried out with a Philips Fm 2401 multimeter.

Electrolyte temperature: range 28C. The electrochemical cell was heated on a hot plate with magnetic stirrer.

Electrolyte: acid leaching solutions from Chuquicamata-Exotica Mine, having the following range of concentration of elements in solution:

Element Concentration Range Copper 15 30 Total iron 9 2O Ferric Iron 2.5 l3

Manganese 4 8 Aluminum l3 21 Sulfuric Acid 28 35 The process is applicable to electrolyte solutions of a much wider range of concentration of elements. Practically acceptable concentrations are:

Copper 2 50 gpl 30 Total iron 0 40 gpl Ferric iron 0 40 gpl Manganese 0 20 gpl Aluminum 0 30 gpl Sulfuric Acid 15 300 gpl Copper sulfides: two kinds of copper concentrates were used, Chalcocite as main constituent:

A Concentrate: 66% Cu B Concentrate: 48.2% Cu The amount of copper in the dispersed particles may vary according to the quality of technical copper sulphide flotation concentrates (25-60%).

The following picture includes main conditions and general results for 4 runs that are representative of the approximately 60 total runs performed:

Run Number Kind of copper concentrate A A A B lnitial copper concentration in electrolyte (gpl) l8.4 17.0 17.0 16.3 Sulfide copper concentrate content in electrolyte (gpl) 7.0 10.0 15.0 10.0 Time (hours) 16 16 48 16 Extracted copper from sulfide Ratio: 23 37 31 34 quality standpoint, to copper of good standards from conventional electrowinning processes, and the efficiency of production is much improved.

EXAMPLE 1 About laboratory runs were carried out. The labo' ratory equipment was mainly a one liter cylindrical electrochemical cell with electrodes 10 centimeters high and 2 centimeters wide.

Total copper deposited The following data concern run number 4. Initial conditions, results and sulfide copper dissolution are included:

Initial conditions p Temperature: 30C

Voltage: 2 Volt Magnetic stirring (glass covered stirrer) Run time: 16 hours Results Total copper deposited: 8.66 grams Final copper concentration in the electrolyte: 10.6

Current efficiency: 84%

Average current density: 20 Amp/square foot.

Sulfide dissolution Ratio: c/a (91:) 8 66 EXAMPLE 2 PILOT PLANT RUNS Equipment and operation Electrolytic cell: lead material according:

length 140 centimeters width 71 centimeters height 91 centimeters Electrodes: 25 centimeters wide, 30 centimeters high, 5 anodes and 4 cathodes were used.

Anode (insoluble): same as Example 1, 8.5 mm thick.

Cathode: electrolytic copper starting sheet.

Centrifugal pump to recycle electrolyte in the cell, in closed circuit with an auxiliary tank.

Power source: current rectifier 0-10 volt output, 0-300 Amp.

current. I

Electrolyte: 900 liters, similar to that described in Ex ample 1.

In one run, the following conditions were used and the following results ocurred:

Conditions lnitial copper concentration in the electrolyte: 26.0 p

Amount of copper sulfide concentrate added: 36 kilograms.

Time test: 184 hours Total cathodic area (4 cathodes): 0.6 square meters Electrolyte temperature: 3339C Voltage: 2 volts Chemical analysis of copper sulfide concentrate:

SiO 3.8%

CaO 0.7

Results Copper deposited: 1 1.8 kilograms Final copper concentration in the electrolyte: l6 gpl Average current density: 14 Amp/square foot Chemical analysis of final cathodes:

As 3 ppm Fe 22 ppm Ni less 1 ppm Pb 2 ppm Bi less 1 ppm Te less 1 ppm Sn less 1 ppm Cd less 1 ppm Mn less 1 ppm Ag 0.155 onza/ton S 56 ppm Cl 569 ppm Se 2 ppm Physical quality of cathodes: excellent crystallization and adherence.

Current efficiency: 72%. This relatively low current efficiency (mainly produced by iron corrosion), compared with laboratory test data, is mainly the result of low agitation at the auxiliary tank thereby allowing settling of copper concentrate particles not being recycled to the cell.

0 Ratio: 100 23.7%

The above data shows very clearly the good results which were obtained by simultaneous electrowinning of copper from leaching solution containing solid copper sulfides in suspension, in spite of the presence of excesive concentrations of oxidizing agents in the electrolyte.

- The v main advantages of the present extraction method are:

a. Normal operational electrowinning current and voltage are not affected by presence of sulfide particles. v

" b. No additional energy is needed to dissolve copper sulfides, because the process proceeds practically as an anodic reaction, instead of oxygen evolution from water.

c. Dissolved copper from sulfide is electrochemically deposited directly on the cathode.

d. The diminishing of oxidating agents in the electrodissolution of copper sulfides. results in an increased current efficiency considerably above the normal level of electrowinning without sulfides in suspension.

e. If agitation in the cell is enough to maintain sulfide particles in suspension, no other modifications of the proper cell are needed.

f. Presence of particles (from sulfides) improve agitation, increasing the rate of the electrowinning process.

g. The operation of simultaneous sulfide dissolution and electrowinning is very simple.

It will be obvious to those skilled in the art that various changes may be made without departing from the scope of the invention and the invention is not to be considered limited to what is described in the specification.

What is claimed is:

l. A metallurgical process for the simultaneous re covery in the same electrolytic reactor of a desired metal from solid sulphide compounds of said metal and from a solution containing said metal as a cation, comprising:

providing a sulphuric acid leaching solution obtained from oxide ores of said metal, said solution containing said metal as a cation;

adding to said solution solid sulphide particles of said metal;

providing an electrolytic reactor having a cathode of said metal and an electrolyte consisting essentially of said leaching solution containing said solid sulphide particles;

subjecting said electrolyte to an electrolytic process in said reactor under conditions of agitation sufficient to maintain said solid sulphide particles in suspension in said solution, and

depositing said metal from said leaching solution and from said sulphide particles on the cathode.

2. The process as claimed in claim I, wherein said solution contains oxidizing agents.

3. The process as claimed in claim 2, wherein the oxidizing agents are oxidizing ions of iron, manganese and aluminum.

4. The process as claimed in claim 1, wherein said solution has a concentration of said metal from 18 to 26 grms/lt.

5. The process as claimed in claim 1, wherein said solution has a concentration of sulphuric acid from 28 to 35 grms/lt.

6. The process as claimed in claim 1, wherein said solid sulphide particles of said metal are added to the solution in an amount from 10 to grms/lt.

7. The process as claimed in claim 1, wherein it is provided to the electrolytic process a cathode current density from 14 to amp/square foot.

8. The process as claimed in claim 1, wherein said solid sulphide is a sulphide concentrate.

9. The process as claimed in claim 1, wherein said metal is copper.

10. The process as claimed in claim 1, wherein said metal is any from the group consisting of antimony, arsenic, bismuth, cadmium, cobalt, gold, lead, molybdenum, nickel, palladium, rhenium, selenium, silver, tellurium, tin and zinc.

l 1. In a process for the electrolytic recovery of a desired metal from a solution containing said metal as a cation, said solution being a sulphuric acid leaching solution obtained from oxide ores of said metal, the improvement comprising;

adding to said solution solid sulphide particles of said metal; and

providing agitation sufficient to maintain said solid sulphide particles in suspension in said solution during said electrolytic recovery process, and conducting said electrolytic recovery at a temperature of about 2839C.

12. The process as claimed in claim 11, wherein said solution has a concentration of said metal from 18 to 26 grms/lt.

13. The process as claimed in claim 11, wherein said solution has a concentration of sulphuric acid from 28 to 35 grms/lt.

14. The process as claimed in claim 11, wherein said solid sulphide particles of said metal are added to the solution in an amount from 10 to 15 grms/lt.

15. The process as claimed in claim 11, wherein it is provided to the electrolytic process a cathode current density from 14 to 20 amp/square foot.

16. The process as claimed in claim 1 1, wherein said solid sulphide is a sulphide concentrate.

17. The process as claimed in claim 11, wherein said solution contains oxidizing agents.

18. The process as claimed in claim 1 1, wherein said metal is copper.

19. The process as claimed in claim 11, wherein said metal is any from the group consisting of antimony, arsenic, bismuth, cadmium, cobalt, gold, lead, molybdenum, nickel, palladium, rhenium, selenium, silver, tellurium, tin and zinc.

20. The process as claimed in claim 17, wherein the oxidizing agents are oxidizing ions of iron, manganese and aluminum. 

1. A metallurgical process for the simultaneous recovery in the same electrolytic reactor of a desired metal from solid sulphide compounds of said metal and from a solution containing said metal as a cation, comprising: providing a sulphuric acid leaching solution obtained from oxide ores of said metal, said solution containing said metal as a cation; adding to said solution solid sulphide particles of said metal; providing an electrolytic reactor having a cathode of said metal and an electrolyte consisting essentially of said leaching solution containing said solid sulphide particles; subjecting said electrolyte to an electrolytic process in said reactor under conditions of agitation sufficient to maintain said solid sulphide particles in suspension in said solution, and depositing said metal from said leaching solution and from said sulphide particles on the cathode.
 2. The process as claimed in claim 1, wherein said solution contains oxidizing agents.
 3. The process as claimed in claim 2, wherein the oxidizing agents are oxidizing ions of iron, manganese and aluminum.
 4. The process as claimed in claim 1, wherein said solution has a concentration of said metal from 18 to 26 grms/lt.
 5. The process as claimed in claim 1, wherein said solution has a concentration of sulphuric acid from 28 to 35 grms/lt.
 6. The process as claimed in claim 1, wherein said solid sulphide particles of said Metal are added to the solution in an amount from 10 to 15 grms/lt.
 7. THE PROCESS AS CLAIMED IN CLAIM 1, WHERIN IT IS PROVIDED TO THE ELECTROLYTIC PROCESS A CATHODE CURRENT DENSITY FROM 14 TO 20 AMP/SQUARE FOOT.
 8. The process as claimed in claim 1, wherein said solid sulphide is a sulphide concentrate.
 9. The process as claimed in claim 1, wherein said metal is copper.
 10. The process as claimed in claim 1, wherein said metal is any from the group consisting of antimony, arsenic, bismuth, cadmium, cobalt, gold, lead, molybdenum, nickel, palladium, rhenium, selenium, silver, tellurium, tin and zinc.
 11. In a process for the electrolytic recovery of a desired metal from a solution containing said metal as a cation, said solution being a sulphuric acid leaching solution obtained from oxide ores of said metal, the improvement comprising; adding to said solution solid sulphide particles of said metal; and providing agitation sufficient to maintain said solid sulphide particles in suspension in said solution during said electrolytic recovery process, and conducting said electrolytic recovery at a temperature of about 28*-39*C.
 12. The process as claimed in claim 11, wherein said solution has a concentration of said metal from 18 to 26 grms/lt.
 13. The process as claimed in claim 11, wherein said solution has a concentration of sulphuric acid from 28 to 35 grms/lt.
 14. The process as claimed in claim 11, wherein said solid sulphide particles of said metal are added to the solution in an amount from 10 to 15 grms/lt.
 15. The process as claimed in claim 11, wherein it is provided to the electrolytic process a cathode current density from 14 to 20 amp/square foot.
 16. The process as claimed in claim 11, wherein said solid sulphide is a sulphide concentrate.
 17. The process as claimed in claim 11, wherein said solution contains oxidizing agents.
 18. The process as claimed in claim 11, wherein said metal is copper.
 19. The process as claimed in claim 11, wherein said metal is any from the group consisting of antimony, arsenic, bismuth, cadmium, cobalt, gold, lead, molybdenum, nickel, palladium, rhenium, selenium, silver, tellurium, tin and zinc.
 20. The process as claimed in claim 17, wherein the oxidizing agents are oxidizing ions of iron, manganese and aluminum. 